The US Marine sniper hadn't slept all night, but it was hard to tell under the layers of camouflage face paint.

He was back at home base after a night battle that left some 30 insurgents dead. "Recon found [the insurgents], they were engaged, and then Specter gunships let loose," said the sniper. "They are no more."

The sniper is at the sharp end of an increasingly successful hunt for guerrillas that is giving US Marines pause as they weigh the possibility of an all-out assault on Fallujah.

Tuesday, US troops will begin joint patrols with Iraqi security forces inside Fallujah in an attempt to gradually restore control over the insurgent stronghold without a major attack. Fallujah presents US officials with a difficult nut to crack. They cannot cede control of the city to the 2,000 or so insurgents now there. But a full-scale assault - accompanied by likely civilian casualties - could turn large segments of the Iraqi population against the US, and derail plans to construct a democratic stronghold in the Middle East.

Tough threats from US commanders that insurgents in Fallujah had just "days not weeks" to hand in their weapons gave way over the weekend to a less strident tone.

"If we don't do this absolutely correctly, we will incur damage to the end state we seek," warns Col. John Coleman, chief of staff of the 1st Marine Expeditionary Force that controls western Iraq.

Instead of bringing enough stability to hand over control to a future Iraqi government, he says the stand-off over Fallujah is a very complex "small war" and "we're deep in it."

To decide future steps, all senior US civilian and military chiefs for Iraq met at Camp Fallujah (seven miles east of the city) on Saturday. At the same time, President Bush and his national security aides held a conference call with Gen. John Abizaid, commander of all US forces in the Mideast, to focus on Iraq and Fallujah.

The series of meetings at this base Saturday - which also included local leaders from Fallujah - agreed that joint US-Iraqi police patrols would begin on Tuesday, and that new rules would forbid weapons on the streets. Terms of the ceasefire, which included a handover of all heavy weapons, have not been met.

At 109 American deaths in Iraq already, and hundreds more Iraqi guerrillas and civilians, April is the deadliest month yet. A marine offensive, commanders predict, would be costly - and possibly counter-productive.

Colonel Coleman uses a painting analogy to describe the complexities of the frontline - and how to balance the amount of force used, with the amount of diplomacy. "I'm looking for a Rembrandt solution, and I don't have it yet. I'm still mixing colors and testing strokes," Coleman says. "We can paint by numbers - that's easy, that's what we're best at. But that's not the right solution."

A military solution is always possible, no matter how much time is spent looking for a peaceful way out. "If it fails, I can always go kinetic," Coleman adds. "That's always there."

Marines in this theater - from the top ranks to truck drivers - declare confidently that they could "take down" Fallujah in 24 hours, with "bone crushing" force. But a sense of moderation - and that the solution is somewhere in between - has been growing in recent days.

Delay of any offensive also appears to be paying off. Though insurgents have been able to dig in deeper during the shaky ceasefire, and hone their defenses, US Marines are also taking a toll.

Beside the early Saturday operation that US officers say killed 30 at a farmhouse south of Fallujah - when the 105mm Howitzer and 40mm cannons of the AC-130 Specter gunship engaged the hideout - another battle in the early hours Sunday killed another 11.

Marines spotted a handful of men leaving a mosque with shoulder-held rockets, and engaged them on the northwest edge of the city. More came out of the brush, firing. When the battle was over, according to two American journalists embedded with the unit, the dead guerrillas were lined up and left there - a stark message. A weak rebel counter-attack later fizzled.

"We're doing a great job singling out these insurgents," says Lance Corporal Justin Lapree from Houston, Texas. "Each day, it's baby steps. You've got to crawl before you can walk, and right now we're crawling."

"We came out here to do peacekeeping, but along the way we've been tasked for some war-fighting," says Lapree, of the 2nd Battalion 1st Marine Regiment. "I'm definitely ready to get this over with in a peaceful way, if it can be done. But we're not [the ones] bringing the fight."

The usual gung-ho of some marines is giving way to a recognition of political costs - and that they are chipping away at the guerrillas anyway. "I think what we're doing is the right way to do it - we're creating a rapport. We're not here to occupy," says Staff Sgt. Jason Valez, from New York City. "At the same time, we're not going to be pushed over or bullied. It's definitely going to work, it just takes time.

"Marines have been doing a good job with precise fire," says Sergeant Valez. "We're not just going to roll in."

Coleman says that it will be important that Iraqis are on board with the solution, since the occupation is meant to end: "I don't want to own Fallujah with a bunch of marines down there, who are getting potshots everyday because we didn't take any Iraqis with us."

Lakhdar Brahimi, the United Nations envoy who is helping draft an Iraqi interim government urged the Bush administration Sunday to "tread carefully" in besieged Fallujah and avoid alienating an already angry populace.

Before leaving Iraq he described the siege as unacceptable collective punishment. Asked about that Sunday, Brahimi said: "When you surround a city, you bomb the city, when people cannot go to hospital, what name do you have for that? And you, if you have enemies there, this is exactly what they want you to do, to alienate more people so that more people support them rather than you.

• Material from the wire services was used in this report.

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